1. Field of the Invention
The invention relates to objective assessment of digitally DCT-based encoded video quality. The proposed invention concerns real-time operations on a video sequence. More particularly, the invention relates to measurement methods used to evaluate the encoding efficiency (quality versus output bit rate) of DCT-based codecs such as the MPEG-2, MPEG-4 and H.264 standards.
2. Description of the Prior Art
The existing literatures and/or patents on digital video quality assessment are fairly new.
Digital video feature extraction techniques have also been studied in depth. U.S. Pat. No. 5,446,492 describes an efficient method for extracting features.
U.S. Pat. No. 5,329,379 describes a system and method for measuring fidelity of decompressed video signals and images. The system compares segments of color, luminance, shape, displacement and texture between a decoded image and its original. There is a global comparison or a local comparison mode that is user selectable.
U.S. Pat. No. 6,252,905 has described a real-time system for evaluating compressed picture quality within a video encoder. The system evaluates the quality of the compression algorithm directly after quantization of the frequency components. The system evaluates loss in the quantized signal for different quantization factors and selects the optimal quantization factor for the best quality. In this patent, the original sequence is required to evaluate quantization loss and it is more of an encoder feature. It also evaluates the degradation level in the frequency domain, not in the visual spatial domain.
U.S. Pat. No. 6,285,797 describes a method and apparatus for estimating digital video quality with a virtual video signal. The apparatus comprises a vision pre-processor, a virtual reference generator, a virtual distortion generator and an image quality metric generator. Basically the decoded/degraded sequence is processed to generate a virtual reference image. The virtual reference along with a visual distortion estimate is used to evaluate an image quality metric.
U.S. Pat. No. 6,823,009 describes a more general system for evaluating the degradation of a video image introduced by a digital transmission and/or storage and/or coding system. Again, the analysis is performed in the frequency domain, on the DCT coefficients. The method compares spatial activity levels between an input (unprocessed) sequence and its processed output sequence in a selected area within the image. Again, an original sequence is needed.
U.S. Pat. No. 6,493,023 describes a method and apparatus (DVQ) for evaluating the visual quality of processed digital video sequences. Again, the DCT coefficients are used for the analysis. The system is also used to adaptively control the encoding bit-rate of within a codec for optimal visual quality. The original sequence is required.